Manufacture of metals of high purity



INVE'NTOR 5 Sheets-Sheet 2 c. M. CHERRlER MANUFACTURE' OF METALS oF HIGHPURITY July 19, 1960 y Filed May 9,'195? c. M; CHERRIER 2,945,797 `vMANUFACTURE OFMETALS oF HIGH PURIT'Y j Filed May 9, 1957 `Jlzlly 19,1960 5 Sheets-Sheet-- 'I5v INVENTOR ATTORNEYS heat.

ly uncontaminated silicon.

which termiucludes pulsating-riads the reactionjthe apparatus, thel@ b eeasily keptat roem temperature, .or "mayj even, be

laziali/arf f MANUFACTURE or" MErALs oF HIGHrURITY Claude MichelCherrier, SL Maude,.France, assignor to `Societe 1Anonyme desiManufactures fdes Glaces et Produits Chimiques de St. Gobain, haunyandCirey, Paris, France 'l :Filed May 9,1251, Ser-,umsehen Climfsizi'ri'fy; application 'France May 12,1955? n u f SClumsvicl...ztl41f64tif; 'f

t This invention relates .tofthe manufacturefof metals Yin United SwissPatent O a state of high purity andiv is particularly adapted tothe tproductionh'of high purity silicon. Heretoforeit hasvbeenproposed toprepare-high. purity silicon by reducing vaporphtase silicontetrachloride with z inc at hightemperature or ton decompose a silane byThose methods have the imperfection of involving the contact of solidsilicon'.Y with the wallsof theapparatus at high temperature. The rateof diffusion of foreign atoms intosilicon increases rapidly with theincrease of temperature, sctthatj those methods lalways involve materialrisk of contaminating the silicon with the materials of the apparatuswith which it'comes in'contact.

It is an object ofthis'inventionto'produce substantial- `AnotherQbject'is to produce 'other metals in substantially uncontaminatedstate.V

Another objectisy to eliminate the contamination of silicon and suchmetals by the material of theapparatus in which they are made.` Y Y l Another object isl to decomposefrnetallhydrides in gas trodes. A Y y 1The-objectsas tofprocess are accomplished, generally speaking,bydecornposinga `silane' or a gaseous hydride or other' metal byinduction, an electrical discharge being phase at low temperature andinapparatus freeof elecwithin `the ga's itself withoutusing electrodeswhich contactthe gas.` f The process `is"earriedoutin `apparatus havinga reaction chamber throughwhichthesilane or other metal hydride in gasphase is passed, under preferably 'reduced`prssure,containinglnofelectrodesincontact with the gas as they would be sourcesof contamination, and by l inducing electrical discharges,iby anlalternating field, iutheeas- During ofthe reaction', may

coolcdbelow it, so that `the metal `powderformed .does notin contactwith the apparatus, become` contaminated andI is consequently pure.

The electric discharge. may be producedwithin the gasv are considered as`metalhydrides for thefpurposes off-this are those metal ispecification, the best` exampley of which is Spil-1,1,A and igermanium-methane, GeH4, which aregaseousat; ordinary temperature andpressure.

The disintegration by induction maybe carried out at atmospheric`pressure or below; but itis' dcsirabletouse l reduced pressure,pressures below-atmospheric being preof fseveralB megacycles per secondl wIIyFig.` 3i is shown a pulsating current generatoiadapted 2,945,797patented July 19,A 1 seo ferred, Theuseofexcessively low pressurelis notnecessary a's the process goes well at several cm. of Hg. u

Any apparatus capable of inducing an electrical discharge. withinthegases. is useful, but the invention includes novel apparatus ldescribedand shown in, theV drawings; Where-intl? t t Fig. yl is a diagrammaticvi W of a simple but success- ""Fig. '2is adiagtallamtic view of'amoreversatile ,apparatus operating by the principles of Fig. l",

` f Fig.l 3 isA ai diagramjof an apparatus operating bypulsatiug"=currentfwith'.Wave lengthen the order of.` a meter totl-kilometer:

" F' `tis` 'a diagram of'an apparatusiof pulsating type generating'waves of length on the orderof centimeters;

electrical supply of the apparatus of Fig. 4;

Ji1`fig1 5. 'is a diagram ofa wave generator suited tothe f Pig; 6 is acompletedV diagram of apparatushblocled outiu FigE l5- Y Y "Referringnow to' the construction ofFig. '1, there is at 50 a source Qfhighfrequency alternating current of continuous wave vOrreversingtyp'elwhich supplies an induction coil 53gwhich is coiled about ahorizontal tube 54. (of quartz,` glass, plastic) through which a currentof a silane may be passed at less'than atmospheric pressure.

Evavcua'-tion means and* gas supply means are well known and are notshown in the drawing. The'vpower sent tothe coil 53 is sufficient toinduce an electrical discharge that illsthe tube. For example,for-500liters per hour of `:silanef or germanium methane'passingthrougha tubefof from, `ZO-'SV'On-im. diameter ata pressure `of about 211cm.:`of Hg, onemay use 5 kilowattsjat a frequency of oscillations ,of 3megacycljes persecond. This is the.l simplest form of'successiulVapparatus. As thegas progresses through the tube, part of it isdisintegrated hyA the discharge, releasinghydrogenand'depositingl'netallicV Si; in a pure lstat p r A fto Aaise itstemperature close vtothepoint of contaminatiiofl, l. j

i Th? Cil-Trent generatingrmeans between C Vand D on the AThetuhe ,canbecooled 'iffthe power usedt'ends `,drawing-Vrnay be of ordinaryconstruction, suchy as is de- 'scribed in'` Radio Engineers" Handbook,F. E,.f"l`er`ri;1 an, "19432- When Vvacuum is` used, as' `it is theIpreferred formof theinvention, itis applied by ajpunhpjV a cold trapbeing intrlduced'inthe pump line, this= beingstandardlowpressuretechnique` and notillustrated". i* f Iriflig.4 2 'an'apparatus of similar electricalconstruction but"'mpre'versatile. Itincludesa source of, s ilan'l which" supplies fa pipe "'2" throughvalves 6i and 7 with he "gas, 'which is delivered/to a reaction chamberV31 bout which is-wound an'induction coil 4 ijssgupplie high frequencyalternating current through terminals() and'Df The lower part `3a1of`the vessel 3 is removable to permit 'the occasionalemptyingof depositedmetal. 'A source Aof suction "10' reduces `the 4pressure u /ithin thevessel 3, a manomete'r-S reveals the pressure inthe system, a very smallpipe 9 with a tiny 'oriiioe cooperates with theV suction means v10 tomaintainY a pressure of'severalgentimetersf o f Hg in the apparatus,large reservoir or tpfessure. ddm :5. Serves tl regulate? thefflw of;Silea@ V*by absorbing diierencesin pressure andrateoiiow. The reactionchamber is withinfan enclosure 11 which can be cooled if necessary ordesirable to reduce the temperature of the reactionvessel. 'I'hereactionmay he arrested asf during theemptyingyof 3a.U Cooling rnea'usdesignated Si), inthe' form of' ai' refrigerator coilj'is lshownsurroundihg t'container 11` in Fig. 2. It is assumed thatQ-D in Fig.; 2

are?connected to Vthe source v50` `of` Fig; :urent maybe presumed, forthese figures, to be on the order to be Vattached at C1D1 totheterhainals GD 'of Figfsfl nected to an oscillationgenerator 22wherein it undergoes successive transformation in the several stages.The apparatus 21, 22, 23 is suiciently well known to need no detaileddescription, yet itmay. be stated that it includes, in sequence, a stagelimiter, a deviation circuit, a

stage limiter, an amplifier, a stage basculer, andY a stage amplifierwhich is connected vto the modulator 23. The

current from modulator 23 Ais put out as impulses of negative voltagesucient to insure unblocking. ,The modulator 23 may be constituted bytwo stage amplitiers'placed in series supplying a circuit including acondenser 24 and an inductance 24a of which the discharge producespulsations supplying the plate 25a of tube 25 of oscillator 26.

.Oscillator 26 includes a tube 25 in a tuned circuit includng in thecircuit the anode 25b, plate 25a, condenser 28, and inductance 27 inparallel, and a reaction inductance 29v connected tothe grid. The triode25 in an actual apparatus furnished a power of 100 kilowatts in asequence of impulses of 3 microseconds. The frequency of recurrence was1000 cycles per second; the frequency of use Vwas 30 megacycles. Theinduction coil 30 is activated lby the impulses from coil 27 anddelivers its potential to terminalsC1D1 which may be connected to C D ofFig. 2 or Fig. 1. VSuch apparatus serves to produce wave lengths on theorder of a meter to a kilometer.

If shorter Wave lengths are desired, e.g. measured in centimeters ratherthan meters, one may employ wave guides and resonant chambers, anexample of vwhich is shown in the novel apparatus of Figs. 4 and 5. Inthose figures an alternator'32, driven by a motor 31, providesalternating current, e.g. of 500 periods per second, to a high tensiontransformer 33 .which delivers the output to a voltage doubling circuit34. The undulating current thus produced supplies an artilcial line 35composed of i resistancesandcapacities in parallel (as inFig. 3) which fdischarge across a pulsation transformer 36 with a perio- Xdicityestablished by rotary sparking means y37 connected lto ground between 34and 35 and including tungsten bars spaced about the periphery of a wheelVrotated by 'motor 31. Opposed bars are connected together' and 4connectthe line 37a to ground intermittently as the Wheel 37 turns, by sparkswhich-close the discharge circuit of the line. Thus very high voltageimpulses are sent to the pulsation transformer 36,- which charges themagnetron 38which, at each pulsation, emits high '.frequenc'y waves 'ofvthe order of 3000 megacycles.

The high frequency energy is transmitted to the resonant chamber (Fig.4) as the high frequency wave is radiated from the end 38(a) of themagnetron, which is a small ball supported within the wave guide 39. Thetuning of the waves emitted by the magnetron-guide is done by aregulatory piston 40 placed at one extremity.

In orderto transmit the power continuously from the magnetron to thechamber 45 on one side and the absorption fixed charge 44 on the other,which may be a mass of water or graphite, and this in proportionsdecided on in advance, one uses a power divider 41 comprising two`tuning pistons 42, 43, one on each side of the guide containing themagnetron, which are made by regulation to dividethe power between 44and 45 as desired. The

axes of the pistons are desirably spaced by a distance of grated, underreduced pressure.

This wave generating apparatus is representative of a known type forgenerating high-frequency oscillations and has its principles disclosedin M LT., vol. 5, chapter 6, page 175; vol. 5, chapter 7, page 224; vol.5, chapter 8, page 275; and M.I.T.vol. 6, Magnetron. Thus, the wavegenerating apparatus, per se, is not claimed to be new but it isbelieved to be new in its structure for, and its application to, thedisintegration of metal hydrides.

The following examples illustrate the invention without limiting thegenerality of what is elsewhere herein stated and claimed.

Example 1 Using an apparatus of the type` of Fig. 2 having a coil 4 often turns of y10 cm. diameter through which a continuous, alternating,high-frequency current is sent from a 5 kilowatt generator with afrequency of 3 megacycles per second. These turns produce discharges inrings in the reaction chamber. The reaction chamber has a volume of 200cm. and, is traversed by the silane under a pressure of 5 cm. ofmercury. The rate of gas flow, instituted by a piston pump, not shown,is about 500 liters per hour measured at atmospheric pressure. Thequantity of .silicon recovered per hour of operation is about 150 grams,which represents a yield of about 24% with relation to the silanedecomposed.

Example 2 The apparatus is described rin Figs. 4 and 5. The silanepasses through a tube 48 of 5 cm. diameter which intersects the Waveguide. The wave guide receives impulses of a duration of 1 microsecondwith a frequency of repetition of 500 pulsations per second; the wavepower is l megawatt, and the carrier wave frequency is of 3,000megacycles per second for a wavelength of l0 cm.; the mean power =in theWave guide is thus about 500 Watts.

The silane is sent through the apparatus at about 200 liters of gas perhour measured at atmospheric pressure. The quantity of silicon recoveredat the end of 2 hours of operation is about 95 grams, which indicates 'ayield of about 19% With respect to the silane decomposed.

The foregoing examples have described the manufacture of extra puresilicon by the decomposition of a silane. The invention has a moregeneral character and isv applied in an analogous way to the manufactureof other metals susceptible of forming stable gaseous hydrides. The

' process is particularly adapted to the production of germanium by thedecomposition of germano-methane (GCH4). The following example`illustrates the manufacture of germanium; Y

Example `3 Using the apparatus'of Example l in which a l-kilo- Wattgenerator sends a high-frequency current of continuous .Waves with afrequency of 500 kilocycles per second, there was produced for a rate ofgermano-methane supply of 250 liters per hour measured at atmosphericpressure,- after 1/2 hour of operation, 117.5 grams of germanium, whichindicates a yield of 29% based on the germano-methane decomposed.

An advantage of the process resides in the fact that the reactionchamber may easily Vbe maintained at room temv perature or below, sothat the contact of the silicon A powder with the walls of the apparatusdoes not induce any/'contamination ofthe product.

Other advantages of the invention are derived from the novel apparatuswhich has been conceived for carrying by the disintegration-of theirgaseous hydrdes, preferably art reduced pressure.

'I'he apparatus described is adapted to carry out the process at highpressure, atmospheric pressure, and re duced pressure. IIt may be easilyregulated to produce optimum conditions of reaction. Itis adapted toproduce whatever wave lengths are preferred for and most eicient in thedestruction of particular silanes and other metal hydrides. l

As many apparently widely different embodiments of the present inventionmay be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments.

What is claimed is:

1. The method of producing elementary metals and metalloids in a stateof high purity which comprises owing through an inert reaction zone,which is protected from contact with contaminating substances by aninert wall, a continuous current of a hydride of an element from theclass of metals and metalloids in gas phase, and inducing in the gasitself within the zone an electrodeless discharge by imposing upon thegas, through the wall, an alternating electrical field.

2. The method of producing elementary metals and metalloids in a stateof high purity which comprises establishing an inert reaction zone,owing a current of a hydride of an element from the class of metals andmetalloids in gas phase through the inert zone, and inducing in the igasin the zone, from outside the zone, an alternating electrodelessdischarge.

3. The method of producing a high purity metal as defined n claim l,which comprises maintaining all objects within the reactor, includingthe inner surface of the reactor, which are in contact with the metallicproducts formed by the action of the electrical discharge upon thehydride, at a temperature below that at which contamination of theproduct by such objects occurs.

4. The method of producing a high purity metal as defined in claim l,which comprises reducing the pressure within the reactor belowatmospheric pressure during the action of the electrical discharge uponthe hydride.

5. The method of producing a high purity metal as defined in claim l,wherein the metal is silicon. 5 6. 'Ihe method of producing a highpurity metal as defined in claim 1, wherein the metal is germanium.

7. The method of producing a high purity metal as defined in claim 1,wherein the metal hydride is a silane.

8. The method of producing a high purity metal as de- 10 fined in claim1, wherein the metal hydride is germanomethane.

References` Cited in the tile of this patent UNITED STATES PATENTSMellor: Comprehensive Treatise on IInorganic and Theoretical Chemistry,vol. 6, 1925, page 219.

Dufour: Competes Rendus, vol. 138 (1904), pp. 1169- 1170. 35 'OgierzComptes Rendus, vol. 89 (1879), pp. 1068- Berthelot: Annales de Chimieet de Physique (5th series), vol. l0 (1877), pp. 75-82.

Ogier: Annales de lChimie et de Physique (5th series), 40 v01. 2o(1880), pp. 33-34.

1. THE METHOD OF PRODUCING ELEMENTARY METALS AND METALLOIDS IN A STATEOF HIGH PURITY WHICH COMPRISES FLOWING THROUGH AN INERT REACTION ZONE,WHICH IS PROTECTED FROM CONTACT WITH CONTAMINATING SUBSTANCES BY ANINERT WALL, A CONTINUOUS CURRENT OF A HYDRIDE OF AN ELEMENT